A spa is a large whirlpool bath capable of seating between two and eight persons in which water is circulated by means of venturi jets. A heater is standard equipment in all spa installations. The heater is used to heat the water. A form a water thermostat known as an "aquastat" is provided which intermittently activates the heater when the water temperature drops below a preset level. A pump is provided which is set on a timer and circulates water through the venturi jets when persons are using the spa.